As an example of a compound semiconductor light-emitting device, a structure has been proposed in which an n-type gallium nitride compound semiconductor layer and a p-type gallium nitride compound semiconductor layer are formed on a substrate. In recent years, gallium nitride (GaN) compound semiconductor light-emitting devices have drawn attention as short wavelength light-emitting devices. The gallium nitride compound semiconductor light-emitting device is formed by laminating an n-type or p-type semiconductor layer and a light-emitting layer on various kinds of substrates, such as a sapphire single crystal substrate, an oxide substrate, and a group III-V compound substrate, by a metal organic chemical vapor deposition (MOCVD) method or a molecular beam epitaxy (MBE) method.
The gallium nitride compound semiconductor light-emitting device is characterized in that, in order to improve emission efficiency, a transparent electrode is used such that light emitted from a light-emitting layer immediately below the electrode is not shielded by the electrode, which makes it possible to effectively emit light from the light-emitting device to the outside.
In the related art, a transparent positive electrode composed of the transparent electrode has a laminated structure of, for example, a Ni or Co oxide layer and an Au contact metal layer. In addition, in recent years, a technique has been proposed which uses as a positive electrode a laminated structure of a layer formed of a transparent conductive oxide material, such as ITO (In2O3—SnO2) and a contact metal layer having a very small thickness, thereby improving transmittance and the emission efficiency of light from a light-emitting layer to the outside.
However, when a transparent electrode formed of a transparent conductive oxide material, such as ITO, is formed on a p-type gallium nitride compound semiconductor layer and a bonding pad for connection to an external electric apparatus is formed on the transparent electrode, it is difficult to obtain a good ohmic contact and strong bonding strength between the transparent electrode and the p-type semiconductor layer, and it is difficult to sufficiently reduce the contact resistance of an interface. As a result, the driving voltage Vf (standard forward voltage) of the semiconductor light-emitting device is increased, and the brightness of light is lowered. In addition, the transparent electrode is likely to be peeled off from the p-type semiconductor layer during wire bonding due to a load applied to the bonding pad.
In order to solve the problems, a semiconductor light-emitting device 108 having the structure shown in FIG. 4 has been proposed in which an n-type semiconductor layer 101 is formed on a sapphire substrate 100, a p-type semiconductor layer 103 and an electrode pad 104 are partially formed on the semiconductor layer 101, a transparent electrode 105 made of ITO (indium tin oxide) is formed on the p-type semiconductor layer 103, a contact hole 106 is formed in a portion of the transparent electrode 105, and a bonding pad 107 is directly connected to the p-type semiconductor layer 103 through the contact hole 106 (see Patent Document 1).
As such, when the bonding pad 107 is directly connected to the p-type semiconductor layer 103, the bonding strength of the bonding pad 107 to the p-type semiconductor layer 103 is stronger than that to the transparent electrode 105. Therefore, even when the bonding pad 107 is pulled by a wire during wire bonding, the bonding pad 107 is not peeled off.
[Patent Document 1] JP-A-7-94782